Factors affecting the quality of direct reading spectrometer analysis

1 , argon

The main function of argon blowing is to drive off the air in the spark chamber when the sample is excited, and to reduce the absorption of the ultraviolet light in the ultraviolet region. Mainly because the oxygen and water vapor in the air have a strong absorption band in the far ultraviolet region, which has a great influence on the analysis result, and is not conducive to the excitation stability, forming or strengthening the diffusion discharge, and generating white spots upon excitation. Therefore, the purity of argon must be required to reach 99.996% or more. In addition, the pressure and flow rate of argon also have an effect on the quality of the analysis. It determines the impact of argon on the discharge surface. This excitation capability must be appropriate and too low to adequately generate oxygen during the excitation of the sample and it. The formed oxide is washed away, and these oxides agglomerate on the surface of the electrode, thereby suppressing the continued excitation of the sample; if it is too large, it causes unnecessary waste. Second, there is also a certain damage to the spectrometer. Therefore, the argon pressure and flow rate must be appropriate. According to practice, the pressure and flow rate of argon should be adjusted according to different materials. For the analysis of medium and low alloy steel, the argon pressure of the input spectrometer should reach 0.5-1.5 MPa, and the flow rate of dynamic argon should be 12-20 readings. The flow rate of static argon is 3 to 5 readings.

2 , slit

The spectrometer uses a complex and sensitive optical system. The ambient temperature, humidity, mechanical vibration, and changes in atmospheric pressure of the spectrometer cause small changes in the line that cause spectral line shifts. Changes in air pressure and humidity change the refractive index of the medium, which causes the line to shift. The increase in humidity not only increases the refractive index of the air, but also corrodes the optical parts, reducing the light transmittance and humidity of the instrument. Generally should be controlled below 55% -60%. The influence of temperature on the grating mainly changes the grating constant, which causes the amplitude of the role to change, resulting in spectral line shift. These changes can cause the spectral lines to not be perfectly aligned with the corresponding exit slits, thereby affecting the analysis results. Therefore, the optical system is adjusted at least once a day if the indoor temperature control is constant. Even if the weather does not change much, adjust the slit twice a week.

3 , the lens of the entrance window

The lens that leads to each chamber, especially the lens that leads to the air chamber, causes argon to be blown when the sample is excited, so that the dust generated when the sample is exposed is blown onto the lens to prevent the transmission of light, which affects the accuracy of the measurement result. Sex. Therefore, it should be cleaned frequently, usually twice a week, to keep it clean, to ensure that all light passes through the lens and enters the light chamber for measurement. It is especially reminded that after cleaning the lens, several waste samples should be excited, and the standardization operation should be performed after the strength is stabilized, otherwise the quality of the analysis will be affected.

4 , the excitation table

Cleaning the inner surface of the excitation table is mainly to avoid the influence of the dust discharge on the residual inner wall. Usually it should be cleaned once every 100-200 times. The distance between the electrode and the excitation surface must be adjusted according to the pole distance requirement. If the distance from the excitation surface is too large, the sample is not easy to be excited. If the distance between the electrode and the excitation surface is too small, the discharge current during exposure is too large, so that the discharge current is too large. Does not match the parameters of the instrument, so there is a difference between the measured results and the actual results, affecting the accuracy of the measurement. Therefore, the distance between the electrode and the excitation surface must be adjusted accurately. After cleaning the excitation stage and the electrode, this problem must be taken seriously.

5 , the correction of the working curve

Although the photoelectric direct reading spectrometer method is not limited by the photosensitive plate, after the working curve is drawn, the curve will change after a period of time. For example, the pollution of the lens, the contamination of the electrode, the change of temperature and humidity, the influence of argon, the fluctuation of the power supply, etc., can change the curve. The position of A in the original graph, after a period of time, the curve may drift to the position of B. In order to use the curve for analysis, it is necessary to try to restore curve B to the position of curve A. To do this, the work curve must be standardized. In the standardization of curves, the following points must be noted:

(1) After cleaning the sample excitation stage, it must be excited more than 10 times or argon gas for one hour before daily standardization work can be done.

(2) The standardized sample should be uniform, the sample preparation should be careful, the surface of the sample should be flat, and the grain should be cleaned. The analysis gap is accurate and the sample holder is kept clean.

(3) The normalized frequency is determined according to the number of samples analyzed. Generally, it must be standardized twice a day.

6 , control sample

In actual work, the working curve often changes due to the metallurgical process of the sample and the standard sample and some physical conditions. Usually, the standard sample is mostly forged and rolled, and the daily analysis is cast. In order to avoid the influence of the metallurgical state change on the analysis results, it is often necessary to use a control sample with the same metallurgical state and physical state as the analytical sample to control the analysis results. The element content of the controlled sample should be within the range of the working curve. And the closer to the content of the analytical sample, the better. At the same time, the element content of the control sample should be accurate and reliable, the composition of the composition is uniform, and the appearance is free of physical defects such as pores, blisters and cracks.

7 , sample

The quality of the spectral analysis depends largely on the sample, and attention should be paid to the preparation and processing techniques of the sample. The lack of a flat surface due to stomatal segregation or the absence of sample placement, as well as errors due to operational errors, can have a significant impact on the quality of the analysis. Therefore sample processing must meet the following requirements:

(1) The entire sample surface should be uniform (the shape is suitable for the excitation table so that the gas flushing chamber can be sealed).

(2) There is no blisters.

(3) Clean the scale and oil on the back of the sample to ensure good contact between the sample and the excitation table.

(4) The surface of the sample should not be contaminated, and the sample should have a grain.

(5) When the sample is excited, the excitation point is generally located at 1/2 of the sample radius, where the chemical composition is relatively uniform, and the result is representative of enthalpy, and the measurement accuracy is high. In summary, through years of practice, several factors affecting direct reading spectrometry have been summarized, which have important application value for improving the quality of elemental analysis.

This article is reproduced from: http://